Industrial technique

ABSTRACT

To compensate for the different motions that two expanding and contracting flues impose on an interconnected communicating duct, three center pinned expansion joints are added to the ductwork. Each of these expansion joints, coupled to adjacent duct segments, enable the duct to adjust to all axial, rotational and togglelike motions that result from movement of the associated flues. This adjustment is accomplished, moreover, without distorting, warping, or shearing the casing.

Elite States Stanley atet 1 Dec. 3, 1974 INDUSTRIAL TECHNIQUE [75] Inventor: Russell A. Stanley, Uniontown, Ohio [73] Assignee: The Babcock & Wilcox Company, New York, NY.

[22] Filed: May 29, 1973 [21] Appl. No; 364,448

Related US. Application Data [63] Continuation of Ser, No. 212,393, Dec. 27, 1971, abandoned.

[52] U.S. C1 110/56, 285/114, 285/227 [51] Int. Cl. F231 9/00, F161 51/02 [58] Field of Search 285/1 14, 226, 227, 228,

[56] References (Iited UNITED STATES PATENTS 1/1953 Jackson 285/227 X 12/1962 Adams 285/114 FURNACE 3,730,566 5/1973 Kazmierski et a1. 285/229 FOREIGN PATENTS OR APPLICATIONS l/l924 Great Britain 285/226 Primary Examiner-Mervin Stein Assistant Examiner-David H. Corbin Attorney, Agent, or Firm-J. M. Maguire; .1. P. Sinnott 5 7 ABSTRACT To compensate for the different motions that two expanding and contracting flues impose on an interconnected communicating duct, three center pinned expansion joints are added to the ductwork. Each of these expansion joints, coupled to adjacent duct segments, enable the duct to adjust to all axial, rotational and togglelike motions that result from movement of the associated flues. This adjustment is accomplished, moreover, without distorting, warping, or shearing the casing.

1 Claim, 1 Drawing Figure INDUSTRIAL TECHNIQUE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to conduits, and more particularly to ducts that provide fluid communication between two relatively moving flues, and the like.

2. Description of the Prior Art Communicating ducts often are used to connect large flues in many industrial -establishments. Frequently, two flues. may be subject to generally unpredictable ranges of relative motion. These motions might result, for example, from thermal expansions and contractions, wind loadings, and the like. These relative motions can warp and perhaps rupture the flues and the connecting duct if the full extent of the movement was not anticipated in the design.

This difficulty is especially noticeable in the air and gas handling systems that are needed for large commercial and public utility boilers. As described, for example, in the Hardgrove U.S. Pat. No. 3,048,131, granted on Aug. 7, 1962 for Method For Burning Fuel, and assigned to the assignee of the instant invention, oxides of nitrogen (N and other atmospheric pollutants can be reduced in effluent combustion gases through the introduction of a final volume of air into the furnace to complete the burning process at some distance from the points at which the initial fuel-air mixture is injected. I

This secondary air usually is channeled into the furnace through a large flue. In some systems, moreover, atmospheric pollutants are further reduced through mixing some of the stack gases with the secondary air in order to circulate these gases through the furnace. These flues are equipped with an intercommunicating duct that enables some of the stack gas to flow into the secondary air flue. Clearly, these flues and the communicating duct each are subject to pronounced temperature differences, cg. boiler casing, air heater, stack gas and ambient temperatures that vary even further in response to furnace operating conditions. The thermal expansions and contractions that these temperatures cause in the flue and duct system can, in all but the most simple installations, cause relative motions in the conduits that defy theoretical analysis.

To prevent these motions from warping, distorting or even rupturing the conduit casing, two expansion joints often are added to the communicating duct.

A typical expansion joint for the application has a relatively short, flexible, accordion-like metal conduit. The ends of this conduit are joined to respective segments of a duct. The two duct segments, moreover, are

- linked together across the flexible conduit by means of pins." Usually, in an installation of the type under consideration, one of the expansion joints is center pinned." A center pinned joint links the duct segments together in a way that restricts them to a pivotal motion. This pivotal motion expands the flexible conduit on one side and compresses the conduit on the other side, i.e., causes the joint to toggle. The other joint in the duct connects adjacent segments through a slotted pin arrangement that not only permits toggle motion but also provides a limited degree of expansion and contraction in the direction of the flexible conduits longitudinal axis.

Through the years various techniques have been developed to estimate the proper sizes'for these expansion joints in order to satisfy the needs of specific installations. In many respects, however, these rules of thumb are unsatisfactory because it is not entirely certain that a particular design will be capable of withstanding the forces that might be encountered.

Accordingly, there is a need for what might be termed a universal joint for a communicating duct in a flue system. This universal joint should be able to convert, absorb, or dissipate the forces generated through a'broad range of flue movements without dis torting, warping, or rupturing the duct casing.

SUMMARY OF THE INVENTION These problems that have characterized the prior art are, to a large extent, overcome through the use of I three center pinned expansion joints. The three joints are coupled to segments of the duct, the adjacent segments permitting only a toggle motion for the respective interposed flexible conduits in the joints.

It has been found, through actual experiment, that this structural arrangement copes with all axial, toggle, and rotational forces that are imposed as a consequence of the movements of the communicating flues.

These forces appear to be dissipated through the toggle motions of the three expansion joints.

Thus, the invention provides a substantially more effective technique for accommodating the effects of compound flue motions on a communicating duct.

.The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE of the drawing shows a typical arrangement that illustrates principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS flue 10 preferably directs high pressure air from an air heater (not shown) in the last heat trap between the boiler and stack to one or more furnace air ports (also not shown) for N0 control. Ordinarily the secondary air flue 10 is subjected to different temperatures, depending on operating conditions. It is primarily because of these temperature differences that the thermal expansion and contraction properties of the flue material cause the flue 10 to undergo a substantial amount of physical movement.

As hereinbefore mentioned, some of the gases discharged into the boilers smoke stack are circulated back through the furnace to further reduce pollutants. Accordingly, a gas circulating flue 11 draws some of the gases from the stack (not shown) and mixes these gases with the secondary air in the flue 10.

The gas circulating flue 11 also is subject to different temperature ranges and from time to time, undergoes different thermal expansions and contractions.

An interconnecting duct 12 is provided to promote fluid communication between the circulating gases in the flue l 1 and the secondary air flue 10. The places of duct attachment on the flues and 11, moreover, have communicating ports that permit the free flow of gases through the system.

In accordance with the invention, the duct 12 is divided into segments 13, 14, and 15. The first of the three duct segments, segment 13, is a transition piece that matches an aperture (not shown) in the secondary air flue 10 to a first center pinned expansion joint 16. One side of the flexible conduit in the expansion joint 16 engages the duct segment in a gas-tight coupling. The other side of the flexible conduit in the joint 16 also is coupled in gas-tight relation to the next adjacent segment 14 of the duct 12.

In keeping with another feature of the invention, the first expansion joint 16 is fixed pinned or center pinned between the adjacent duct segments 13 and 14 by means of a linkage 17 that is shown schematically in the drawing. Although the joint 16 can toggle, the linkage 17 prevents the flexible conduit from longitudinal expansion or contraction. Thus, as the duct segment 13 moves in response to the combined motions of the flues 10 and 11, the flexible conduit in the joint 16 is limited to simultaneous expansion and contraction on opposite sides of the surface to produce a wedge-shaped appearance.

In a similar manner, a second center pinned expansion joint 20 is interposed between adjacent duct segments 14 and 15. The joint 20 also prevents longitudinal expansion of the interposed flexible conduit, although permitting the conduit to toggle and assume the wedge-shaped appearance described above as a consequence of the flue movements.

Further, in accordance with the invention, a third expansion joint 21 couples the duct segment 15 to an aperture (not shown) in the gas circulating flue 11 by means of fixed or center pins that are secured to an adjacent portion 18 of the flue 11 and to the adjoining part of the duct segment 15. In the embodiment of the invention shown in the drawing, the duct segment 15 is illustratively presented as an ell section that negotiates a 90 turn in the direction of the duct 12. As described in connection with the expansion joints l6 and 20, the joint 21 is limited to a toggle motion because of a center pin linkage 19.

Ordinarily the expansion joints 16, 20, and 21 are strong enough to support the entire assembled duct 12. If, however, additional structural support is required for the duct 12, a constant load hanger can be coupled to the duct 12 in order to bear the imposed dead weight load.

In operation, if the secondary air flue 10 is moving in the direction of arrow 22 and the gas circulating flue 11 as moving in a generally opposite direction is indicated by arrow 23, the forces applied to the interconnecting duct 12 by these two motions are dissipated in the toggle action of the expansion joints 16, 20, and 21. It has been found that this physical arrangement copes with all flue movements, axial, toggle, and rotational with-.

out unduly stressing, warping, or rupturing the conduits in the system.

Thus, in accordance with the invention, the center pinned expansion joints are able to accommodate linear motions in three dimensions as well as rotational motion in any direction. This is distinguished from the limited adaptation to compound motions that has characterized the prior art.

The invention further provides a significant economy. The costly ties ordinarily used to cope with most wind, pressure and seismic forces are not needed with the novel structure described herein. The three center pinned expansion joints of the present invention seem to redistribute these applied forces back to the interconnected flues. The slotted pin expansion joint in prior structures, which enjoyed a degree of axial motion necessarily required at least one tie to cope with this motion if, for example, the ducting included a bend. Consequently, this prior structure was not capable of coping with the entire load without at least one tie.

I claim.

1. A duct structure for a boiler having an exhaust stack consisting essentially of a furnace for said boiler, a flue for establishing communication with the exhaust in the stack, another flue relatively movable with respect to said exhaust flue for carrying air into the boiler furnace, said two flues movable relative to each other, said flues each having a respective aperture in the sur- 'face thereof for fluid communication therebetween to carry said exhaust gas into said furnace through said air flue, said exhaust being at a higher temperature than said air, a first duct segment in lateral communication with said air flue by way of said air flue aperture, an intermediate duct segment in communication with said first duct segment, an expansion joint interposed be tween said first and said intermediate duct segments to establish fluid communication therebetween, pin means coupling said segments together to prevent said joint from expanding in an axial direction, another duct segment in fluid communication with said intermediate duct segment, an intermediate expansion joint interposed between said intermediate and said another duct segment to establish fluid communication therebetween, pin means coupling said intermediate and said another duct segment together to prevent said intermediate joint from expanding in an axial direction, a terminal expansion joint laterally coupling said another duct segment to said stack exhaust flue by way of said flue aperture to establish lateral exhaust gas flow into the boiler furnace air flue, and pin means coupling said stack exhaust flue to said another duct segment to prevent said joint from expanding in an axial direction. 

1. A duct structure for a boiler having an exhaust stack consisting essentially of a furnace for said boiler, a flue for establishing communication with the exhaust in the stack, another flue relatively movable with respect to said exhaust flue for carrying air into the boiler furnace, said two flues movable relative to each other, said flues each having a respective aperture in the surface thereof for fluid communication therebetween to carry said exhaust gas into said furnace through said air flue, said exhaust being at a higher temperature than said air, a first duct segment in lateral communication with said air flue by way of said air flue aperture, an intermediate duct segment in communication with said first duct segment, an expansion joint interposed between said first and said intermediate duct segments to establish fluid communication therebetween, pin means coupling said segments together to prevent said joint from expanding in an axial direction, another duct segment in fluid communication with said intermediate duct segment, an intermediate expansion joint interposed between said intermediate and said another duct segment to establish fluid communication therebetween, pin means coupling said intermediate and said another duct segment together to prevent said intermediate joint from expanding in an axial direction, a terminal expansion joint laterally coupling said another duct segment to said stack exhaust flue by way of said flue aperture to establish lateral exhaust gas flow into the boiler furnace air flue, and pin means coupling said stack exhaust flue to said another duct segment to prevent said joint from expanding in an axial direction. 